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Mendelian Disorders

Mendelian Disorders can be defined as a type of genetic disorder that arises due to alterations in one gene or as a result of abnormalities in the genome. Such a condition can be seen from birth and be found based on family ancestry utilizing the genealogical record. The investigation henceforth completed is known as the family examination.

These hereditary problems are very uncommon and may influence one individual in each thousand or 1,000,000. Nevertheless, hereditary issues could also be acquired. Inheritable hereditary issues, as a rule, happen in the germline cells,7 though in non-inheritable, the disorders are, for the most part, brought about by mutations or because of certain defects in the DNA.

For example, the disease may either be brought about by an acquired hereditary condition or by another mutation brought about by ecological causes or something else.

Mendelian Disorders Principle

Mendel's examinations on pea plants with respect to inheritance pattern has given a strong base to our understanding of single-gene illnesses in people. Mutations that occur in a single gene bring about Mendelian Disorder. Mendelian disorders are caused due to mutations at a single locus.

This can occur either on an autosome or a sex chromosome. Pedigree analysis of a family that has a history of Mendelian disorder can be performed to further understand the probability of occurrence in future generations and to identify whether the trait is dominant or recessive.

Mendel’s Law of Segregation

Mendel’s law of segregation states that “At the time of formation of gametes, each gene gets separated so that every gamete has only one allele for each gene.”

Mendel’s Law of Independence

Mendel’s Law of Independence states that “At the time of formation of gametes, the segregation of each pair of gene takes place independently of the other pairs of genes” or simply, the allele which is received by a gamete for one gene does not depend on the allele which is received for another gene.

Types of Mendelian Disorders

  • Autosomal dominant
  • Autosomal recessive
  • Sex-linked dominant
  • Sex-linked recessive
  • Mitochondrial

Common Mendelian Disorders

Some common Mendelian Disorders are:

  • Haemophilia
  • Muscular Dystrophy
  • Sickle cell anemia
  • Cystic fibrosis
  • Thalassemia
  • Phenylketonuria
  • Colour blindness
  • Skeletal dysplasia

Haemophilia

  • This is a type of sex-linked recessive disorder. As per the hereditary pattern, the unaffected carrier mother gives the hemophilic traits to her son.
  • Females are rarely affected by this X-linked genetic disorder. In a family, for the daughter to be haemophilic, the mother has to be a carrier or haemophilic but the father, by all means, should be hemophilic.
  • Haemophilia causes blood clotting issues. In these patients, the blood does not clot ordinarily as the protein that helps in blood coagulation is faulty. Hence, an individual experiencing this infection normally has side effects of unexplained and unreasonable draining of blood from cuts or wounds.
  • This type of hereditary disorder is caused because of defects in the X-linked chromosomes, so naturally, males are more affected than females.

Sickle Cell Anaemia

  • This is a type of autosomal recessive hereditary disorder.
  • According to the Mendelian pattern of inheritance, a sickle cell anaemic individual usually gets the defective gene from both carrier parents.
  • Sickle Cell Anaemia is caused due to change in the position of the 6th amino acid of the beta-globin chain of haemoglobin. Here, the amino acid Glutamate is replaced by Valine.
  • The mutant haemoglobin molecule goes through a physical change that causes the transformation of a biconcave RBC to a Sickle Cell.
  • This sickle celled RBC due to its deformed shape has lower oxygen-carrying capacity than biconcave RBCs.

Phenylketonuria

  • This hereditary disorder is autosomal recessive in nature.
  • Phenylketonuria is an inherited disorder caused by the reduced digestion of the amino acid phenylalanine.
  • In this disorder, the affected individual lacks the enzyme that converts phenylalanine to tyrosine. Accordingly, phenylalanine collection happens in the body and is changed into numerous derivatives which bring about mental retardation.

Thalassemia

  • This is a type of hereditary disorder where the body makes insufficient amounts of haemoglobin. Subsequently, an enormous number of red blood cells undergo destruction and this causes anaemia in patients. Thalassemia causes fatigue, weakness, and paleness.
  • It is an autosomal recessive disorder. There are four different types of thalassemia based on the severity: trait, minor, intermedia, and major.
  • Facial bone deformations, swelling in the abdomen region, and dark urine are some of the symptoms and effects of Thalassemia.

Cystic Fibrosis

  • Cystic Fibrosis is an autosomal recessive disorder.
  • Cystic Fibrosis affects the respiratory and digestive systems. Patients suffering from this hereditary disorder produce huge quantities of mucus that block the passage of the lungs and pancreas.
  • Individuals suffering from cystic fibrosis have an exceptionally short life span.

 

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